1. Field of the Invention
The present invention generally relates to data transmission and reception in a wireless relay system, and more particularly, to a method and apparatus for joint unicast using Multi-User Superposition (MUS) coding.
2. Description of the Related Art
One active research area of a future generation communication system, such as the 4th Generation (4G) communication system, involves providing a large amount of data with various Quality of Service (QoS) requirements at high rates to users. To enable high-speed communications, the 4G communication system uses cells having very small radii. This means that a conventional centralized wireless network designing scheme is not viable for implementation of the system. In this context, there is a need for a wireless network design that supports distributed control and actively copes with changes in a cell environment such as additional installations of Base Stations (BSs). Hence, a self-configurable wireless network is required which autonomously configures a wireless network without control of a central system in a distributed fashion to provide communication services.
Techniques used for an ad hoc network should be adopted to deploy the self-configurable network in the 4G communication system. A major ad hoc network is a multi-hop relay cellular network realized by employing a multi-hop relay scheme to a cellular network system including fixed BSs. Typically, the BSs are fixed in position in the cellular network. The resulting less flexibility in configuring a wireless network makes it impossible to provide efficient communication services in a wireless environment experiencing fluctuating changes in traffic distribution or the number of required calls.
In the 4G communication system, to avert this problem, the self-configuration wireless network uses a relay scheme in which data is delivered over multiple hops through a plurality of neighboring Mobile Stations (MSs) and fixed Relay Stations (RSs), to thereby enable fast network reconfiguration according to environmental changes and enable efficient operation of the overall wireless network.
The multi-hop relay wireless network offers the benefits of cell coverage expansion and increased system capacity. When the channel status between a fixed BS and an MS is poor, a multi-hop link is established between them via an RS so that a better radio channel is provided to the MS. Efficient communication services can be provided, especially in a shadowing area with a severe shielding effect caused by buildings.
The RS-based wireless relay system needs to transmit data from a BS to an intended MS efficiently on the downlink. There exists a need for a technique for increasing overall communication efficiency, especially when the BS serves a plurality of MSs and an RS assists downlink transmissions for MSs having poor direct links to the BS.